Barnacles

Darwin and barnacles

Darwin’s interest in Cirripedia, a class of marine arthropods, was first piqued by the discovery of an odd burrowing barnacle, which he later named “Mr. Arthrobalanus,” while he was aboard the HMS Beagle. After completing four Beagle-related publications, Darwin dissected, classified, and wrote about barnacles on a daily basis from 1846 to 1854. Ultimately, Darwin’s deep and focused research on barnacles resulted in the publication of four serious monographs, which established him as a major figure in the British zoological community. (Darwin’s earlier geological publications had already established him as a man of scientific merit).

Darwin’s microscope slides of barnacles, now at the University Museum of Zoology, Cambridge

Barnacles and speciation

Darwin’s work on barnacles was a key component in the theory of speciation he published in his 1859 magnum opus On the Origin of Species. By studying a group of organisms in its entirety, both living forms and fossilized remains, Darwin was able to see the fascinating variety among related individual forms and to understand how this diversity might have developed over time. In his studies, Darwin classified the various barnacle groups using an innovative theoretical framework. For instance, though he used the term ‘homology’ in some of his work in the standard 19th-century fashion (i.e., the same organ in different animals with a variety of forms and functions), he also used it in a more evolutionary sense by comparing barnacle larvae to adults and by comparing barnacles to crustaceans more generally. Significantly, Darwin’s detailed research into a single class–in this case Cirripedia–provided substantive evidence of the broad and sweeping theory of evolution by natural selection he proposed in On the Origin of Species. This body of evidencehelped Darwin convince his readers of the validity of his ideas.

Barrett, P. H. ed. 1977. “On the Ova of Flustra, or, Early Notebook, Containing Observations Made by C.D. When He Was at Edinburgh, March 1827.” In Barrett, P. ed., The collected papers of Charles Darwin. 2 vols. Chicago: University Press, 2: 285-91. Darwin’s Notes on Flustra

Darwin writes to James Clark Ross, officer in the British navy and polar explorer, asking him to collect and preserve specimens of Cirripidea on his upcoming expedition to the Arctic in search of the lost explorer John Franklin.

Discussion Questions:

1. Why is Darwin interested in the barnacle he eventually names “Mr. Arthrobalanus”? Why do you think this barnacle inspired Darwin to study barnacles for eight years?

2. How does Darwin use correspondence to contribute to his study of Cirripidea? How crucial do you think the specimens and information he obtained through correspondence were to his studies?

3. From what regions does Darwin request barnacle specimens? Why was it necessary for him to have specimens from so many different parts of the world?

4. How did Darwin’s observations of the immense variation in Cirripidea influence his views on the mutability of species? Describe the significance of Darwin’s barnacle work to his ideas in On the Origin of Species.

EXPERIMENT

For one example of a classroom activity, as performed at Harvard, click here!

In this teaching module, you will find the resources necessary to discuss Darwin’s observations and experiments with barnacles, and relate them to his thoughts on speciation. This module also provides an opportunity to examine how Darwin used correspondence to collect specimens and evidence for his scientific work.

1. discuss Darwin’s fascination with barnacles

2. examine the contribution of Darwin’s work with barnacles to his theory of speciation

3. explore the relationship between empirical observation and scientific theory